Dye comprising a chromophore to which an acyloin group is attached

ABSTRACT

The present invention relates to a dye comprising a chromophore to which an acyloin group as anchoring group is attached, to a method of synthesis of such dye, to an electronic device comprising such dye and to the use of such dye.

The present invention relates to a dye comprising a chromophore to whichan acyloin group is attached, to a method of synthesis of such dye, toan electronic device comprising such dye and to the use of such dye.

The dye-sensitised solar cell (DSSC) (B. O'Regan and M. Grätzel, Nature353 (1991) 737; WO 91/16719 [A]) is a photovoltaic device that offershigh energy-conversion efficiencies at low cost. In contrast to thesilicon-based systems, where the semiconductor assumes both the task oflight absorption and charge carrier transport, in DSSCs these functionsare separated. Light is absorbed by a sensitizer dye which is anchoredto the surface of a semiconductor such as nanocrystalline TiO₂. Thecharge separation takes place at the interface via photo-inducedelectron injection from the dye into the conduction band of thesemiconductor. The dye molecule is regenerated from a counter electrodevia a redox couple in the electrolyte. The redox couple is regeneratedin turn at the counter-electrode the circuit being completed by electrontransport through the external load.

The efficiency of a DSSC is determined by the number of collected andinjected photons, and thus by the light absorbed by the dye sensitizer.One of the main criteria of a dye to act as efficient sensitizer in DSSCis its adsorbtion (by chemisorption) onto the semiconductor surface.Further, for high efficiencies, the ideal sensitizer should absorbefficiently over a broad range of solar spectrum. Upon photo-excitationthe dye should inject electrons into the conduction band of thesemiconductor with a quantum yield of unity. To minimize energy lossesduring electron transfer, the energy level of its excited state shouldbe well matched with the lower bound of the conduction band of thesemiconductor. Its redox potential should be well matched with that ofthe redox couple so that the dye regeneration via electron donation ispossible.

The best photovoltaic performance has so far been achieved with carboxylgroups containing polypyridyl complexes of ruthenium (known as red-dyeand black-dye). [M. K. Nazeeruddin, A. Kay, I. Rodicio, R.Humphry-Baker, E. Müller, P. Liska, N. Vlachoppoulos, M. Grätzel, J. Am.Chem. Soc., 1993, 115, 6382]. The photoexcitation of a Ru-complexresults in an intramolecular metal-to-ligand charge-transfer (MLCT)transition. The photoexcited electrons located in the bipyridyl ligandscan be very efficiently injected in the conduction band of thesemiconductor via the carboxyl-anchor groups. This process has beenshown to be very fast. [Y. Tachibana, J. E. Moser, M. Grätzel, D. R.Klug, J. R. Durrant, J. Phys. Chem. 1996, 100, 20056] In contrast, forthese complexes the recombination process between the injected electronsin TiO₂ and the dye-cations is a slow process. The slow recombination isconsidered to be a result of the large separation between semiconductorand the Ru³⁺ by the bipyridyl ligands. Thus, the molecular design ofthese Ru-complexes is successful in an efficient charge separation andthus, high energy conversion efficiency.

However, the energy conversion efficiency of the DSSC is limited by thelight-harvesting capacity of these Ru-dyes to absorb the sunlight. Thephoto-active region of the photovoltaic device is reduced to the visiblepart of the solar spectrum, and within that, to the shorter wavelengthregion. The photons of the longer wavelength region are not harvestedand cannot be converted to electrical energy.

So far most of the dyes employed as photosensitizers in the field ofDSSC have as anchoring group carboxylic acid groups to anchor on tonanoporous semiconductor. This limits the pool of all dyes, organic,inorganic and hybrid that can be used as sensitizer. Other anchoringgroup which show good properties and have been more intensively studiedare phosphonic acid groups (a) Grätzel et al, J. Phys. Chem. B, 2004,108, 17553; b) W. Choi et al, J. Physl. Chem. B, 2006, 110,14792-14799). Adsorption and charge injection could be furtherdemonstrated with other anchoring groups like sulfonic acid, hydroxyl,triethoxysilane, catechol group and boronic acid, but no solar cellswith significant efficiency of DSSC could be achieved with dyes havingsuch anchoring groups (a) Grätzel et al, New. J. Chem., 2000, 24,651-652; b) Ford et al., J. Phys. Chem. B, 1994, 98, 3822; c) Lakhimiriet al., J. Photochem. Photobiol., A, 2004, 166, 91.).

Nanoporous semiconductors, such as TiO₂, are key components in theprocess of heteregenous photocatalysis applied in the field ofphotocatalytic hydrogen production or photolytic water purification(Arakawa et al., J. Photochem. Photobiol. A, 2000, 63-69; b) Chanon,Eds. Elsevier, Photoinduced Electron Transfer, 1988). Mostphotocatalysts, such as nanoiporous TiO₂, are active under UVirradiation, and their inactivity in the visible light region (solarlight) limits their practical application. One of the strategies toovercome this is the anchoring of charge transfer dyes to the surface ofthe wide band gap semiconductor rendering them sensitive to visible sunlight. As above, the dyes are generally linked to the semiconductorthrough a carboxylate linkages via a ester linkage. This linkage isquite unstable in water which is the environment in such processes.There is a need on alternative effective and stable anchoring groups forattaching dyes on the semiconductor surfaces.

Accordingly, it was an object of the present invention to provide forimproved dyes with intense absorption in the visible and long wavelengthregion of the solar spectrum. It was another object of the presentinvention to provide for dyes which can be easily covalently attached tonanocrystalline wide band gap semiconductors, such as TiO₂, SnO₂ etc. Itwas furthermore an object of the present invention to provide for dyesthat allow an efficient charge transfer from the dye to thesemiconductor. It was furthermore an object of the present invention toprovide for dyes that are easily accessible due simple methods ofpreparation.

All these objects are solved by a dye comprising a chromophore to whichan acyloin group is attached, said dye being represented by formula 1aor 1b:

wherein said chromophore is an organic or metal-organic compoundabsorbing electromagnetic radiation in the range from 300-1200 nm, or asubrange thereof, preferably 350-500 nm or 500-750 nm or 350-700 nm,wherein A is selected from H, or any cyclic or acyclic alkyl, or anystraight or branched chain moiety of general formula —(CH₂)_(n1)—R,—[(CR═CR)_(n1)—(CH₂)_(n2)]_(p)—R, —[(C≡C)_(n1)—(CH₂)_(n2)]_(p)—R,—[(CH₂)_(n1)—X_(n2)]_(p)—R, or halogen, such as F, Cl, Br, I, ormoieties containing heteroatoms, such as NO₂, CN, NR₂, —OH or anysubstituted or non-substituted phenyl or biphenyl or heteroaryl, ormoieties forming a ring structure with said acyloin group,wherein, at each occurrence and independently, n1 and n2=0-12,preferably 0-4, p=0-6, preferably 0-2,wherein X is selected from —CR₂, O, S, NR, —CR,wherein R is selected from H or any straight or branched alkyl chain ofgeneral formula —C_(n)H_(2n+1), or —COOR¹, —OR¹, —SR', —NR¹ ₂, or F, Cl,Br, I, O, N, NO₂, CN, CF₃, wherein R¹ is H or any straight or branchedalkyl chain of general formula —C_(n)H_(2n+1), or any substituted ornon-substituted phenyl or biphenyl, heteroaryl, n=0-12, preferably 0-6.

In one embodiment, the dye according to the present invention comprisesa chromophore to which an acyloin group is attached, said dye beingrepresented by formula 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, or 2j

wherein A, X, n1, n2, n, p are as defined above,and wherein Y, at each occurrence, is independently selected from —CR₂,O, S, NR, —CR, R being as defined above.

In one embodiment, the dye according to the present invention isrepresented by formula 2d, 2e, 2f, or 2h

In one embodiment, said chromophore is selected from the moieties shownin formula 3

or any combination of the moieties represented by formula 3, whereinsaid chromophore is linked to said acycloin group by any of the C-atomsor X or Y or R within said chromophore, wherein Z is one or moremoieties which, at each occurrence, is independently selected from H, orany cyclic or acyclic alkyl, or any straight or branched chain moiety ofgeneral formula —(CH₂)_(n1)—R, —[(CR═CR)_(n1)—(CH₂)_(n2)]_(p)—R,—[(C≡C)_(n1)—(CH₂)_(n2)]_(p)—R, —[(CH₂)_(n1)—X_(n2)]_(p)—R, or halogen,such as F, Cl, Br, I, or moieties containing heteroatoms, such as NO₂,CN, NR₂, —OH or any substituted or non-substituted phenyl or biphenyl orheteroaryl, preferably represented by formula 4

and wherein R, X, Y, n, n₁, n₂ and p are as defined in claim 1.

In one embodiment, the dye according to the present invention isrepresented by formula 5

wherein R₁₁, R₁₂, R₁₃, at each occurrence, are independently selectedfrom H or any straight or branched alkyl chain of general formula—C_(n)H_(2n+1), or —COOR¹, —OR¹, —SR¹, —NR¹ ₂, or F, Cl, Br, I, O, N,NO₂, CN, CF₃, wherein R¹ is H or any straight or branched alkyl chain ofgeneral formula —C_(n)H₂₊₁ or any substituted or non-substituted phenylor biphenyl, heteroaryl, n=0-12 preferably 0-6,and wherein X and Z are as defined in claim 4.

In one embodiment, the dye according to the present invention isrepresented by formula 6

or is represented by any of structures 17-26:

In one embodiment, the dye according to the present invention isrepresented by formula 7

wherein R₁₁, Z, and X are as defined in claim 5, or is represented byformula 8

wherein R₁₁, R₁₂, R₁₃, Z, X and Y are as defined above, or isrepresented by formula 9

wherein R₁₁, Z, X and Y are as defined above, or is represented byformula 10

wherein R, Z, X and n are as defined above, or is represented by formula11

wherein R, Z, X, Y and n are as defined above, or is represented byformula 12

wherein R, Z, Y, X and n are as defined above, or is represented byformula 13

wherein R, Z, X, Y, n are as defined above.

In one embodiment, said chromophore is a metal complex selected from thestructures represented by formula 14

(L)_(n3)(L′)_(n4)M(Hal)_(n5)  (formula 14)

M being Ruthenium Ru, Osmium Os, or Iridium Ir, preferably Ruthenium,Hal being independently selected from Cl, Br, I, CN, —NCS, preferably—NCSwith n3, n4, n5 being integers which, at each occurrence, areindependently 0-4, preferably 2 or 3,and L and L′ being organic heterocyclic ligands containing nitrogenatoms which are linked by N-atoms to the respective metal M, and whereineither one of L and L′, or both L and L′ are linked to the acyloin groupby any of the C-atoms within said ligands.

In one embodiment, said ligands L and L′ are independently, at eachoccurrence, mono- or polycyclic, condensed rings or such ringscovalently bonded to each other.

In one embodiment, said ligands L and U are independently, at eachoccurrence, selected from the group comprising

wherein Z is as defined above.

In one embodiment, said chromophore is a metal complex represented byformula 16

(L″)_(n6)M′  (formula 16)

M′ being Palladium Pd, Platinum Pt or Nickel Ni, preferably Pd,and n6 being an integer 0-4, preferably 1-2,and L″ being an organic heterocyclic ligand containing nitrogen atoms,said ligand being linked by one or several of said N-atoms to therespective metal M′, and said ligand being linked to said acycloin groupby any of the C-atoms within said ligand.

In one embodiment, said ligand L″ is selected from the group comprising

wherein Z is as defined above.

The objects of the present invention are also solved by an electronicdevice comprising a dye as defined above.

In one embodiment, the device according to the present invention is asolar cell, preferably a dye-sensitized solar cell (DSSC), said solarcell further comprising a photoactive semiconductor porous material.

In one embodiment, the device according to the present inventioncontains a charge-transporting agent which is a liquid, polymer gelbased or solid state electrolyte.

In one embodiment, the device according to the present invention is asolar cell wherein said dye is chemisorbed to said photoactivesemiconductor porous material.

In one embodiment, the device according to the present invention furthercomprises at least one other dye.

In one embodiment, said at least one other dye is a dye according to thepresent invention.

In one embodiment, said at least one other dye is a dye selected fromstructures 15, 27-32:

In one embodiment, said photoactive semiconductor porous material isselected from TiO₂, SnO₂, ZnO, Nb₂O₅, ZrO₂, CeO₂, WO₃, Cr₂O₃, CrO₂,CrO₃, SiO₂, Fe₂O₃, CuO, Al₂O₃, CuAlO₂, SrTiO₃, SrCu₂O₂, ZrTiO₄,preferably TiO₂, and combinations of the foregoing.

In one embodiment, said photoactive semiconductor porous material hasone or several of the following features:

-   -   a thickness of 1-100 μm, preferably 5-30 μm,    -   consists of one or more layers    -   contains particles having an average diameter or length in the        range of from 1 nm to 40 nm, preferably 15-30 nm    -   is a mixture of at least a first and second kind of particles,        said first kind of particles having an average diameter or        length in the range of from 1 nm to 30 nm, and said second kind        of particles having an average diameter in the range of from 30        nm to 100 nm and/or a length in the range of from 100 nm to 5        μM.

The objects of the present invention are also solved by the use of a dyeaccording to the present invention as a sensitizer in a dye-sensitizedsolar cell.

In one embodiment, said use is together with at least one other dye.

In one embodiment, said at least one other dye is a dye as definedabove, or a dye selected from structures 15, 27-32:

In one embodiment, said use together with at least one other dye is in adye-sensitized solar cell having a tandem geometry (as, e.g., describedin Example 9 below), or the mixture of a dye in accordance with thepresent invention and at least one other dye is used for coating anelectrode of said dye-sensitized solar cell.

The objects of the present invention are also solved by the use of a dyeaccording to the present invention, as a photosensitzer in aphotocatalytic process, such as photocatalysed hydrogen production orphotocatalytic degradation of organic pollutants. It should be notedthat any photocatalytic process may be useful in the context of thepresent invention.

In one embodiment, during preparation of the device, the dye moleculesare adsorbed to the nanoporous particles via self-assembling out of adye solution or a dyes-mixture solution.

Examples of electronic devices comprising a dye in accordance with thepresent invention include energy supply devices for portable electronicdevices and displays, such as solar cell panels for or incorporated inmobile phones, notebooks, laptops, portable audio-tape players,MP3-players, remote controls, e-cards, e-books, e-readers, portableCD-players, portable DVD-players, cameras, digicams, GPS devices,portable sensors, displays integrated in electronic devices. Examples ofelectronic devices in accordance with the present invention also includeportable solar chargers for batteries of any of the afore-mentioneddevices. Moreover, electronic devices in accordance with the presentinvention include smart windows, on-roof-applications, especially inareas where a grid connection is not possible, e.g. camping cars, boats.If the electronic device in accordance with the present invention is anenergy supply device, and said energy supply device is a solar cellpanel, such panel is preferably a dye-sensitized solar cell panel (DSSCpanel) (see also FIG. 21).

The objects of the present invention are also solved by the use of a dyeaccording to the present invention, for the sensitization of thephotocatalyst, such as TiO₂, in photocatalytic processes, e.g inphotocatalysed hydrogen production, photocatalytic splitting of water orphotocatalytic decomposition of pollutants.

As used herein, the term “dye” is meant to refer to a chromophore towhich an acyloin group is attached. The term “chromophore”, as usedherein, is meant to refer to an organic or metal-organic compound whichis able to absorb electromagnetic radiation in the range of from 350 nmto 1100 nm, or a subrange thereof, e.g 350-500 nm or 500-850 nm, or350-850 nm.

An acyloin group is the moiety which is included in the structure of thedyes according to present invention and is represented by formula 18

The term “anchoring group”, as used herein, is meant to refer to anyfunctional group that allows a covalent coupling (chemisorption) of theentity to which such anchoring group belongs, to a surface, for examplethe surface of a nanoporous semiconductor layer within a solar cell.

A dye is referred to as being “chemisorbed” to a layer or surface, ifthe dye is covalently coupled thereto.

With reference to formula 3 which exemplifies a “chromophore” inaccordance with the present invention, the term “a combination of themoieties represented by formula 3” is used. This is meant to encompassany molecule wherein one or several of the structures given in formula 3are covalently linked to each other to also produce a “chromophore”.

The term “substituted phenyl/biphenyl” is meant to refer to anyphenyl/biphenyl wherein a hydrogen has been replaced by a substituent,such as a halogen, NO₂, NH₂, OH or other suitable functional groups.Such substituents have for example been defined above as Z, whichsubstituents may also be substitutents at a phenyl or biphenyl.

The inventors have surprisingly found that using acyloin groups asanchoring groups for a dye allows an efficient covalent attachment ofsuch dye to nanoporous surfaces of photoactive layers, such asTiO₂-layers. The dyes having the acyloin group attached as anchoringgroup can be used as sensitizers in solar cells but also for sensitizingthe photocatalyst which are mosly wide band gap oxide semiconductorssuch as TiO₂, to extend the photocatalytic activity of thephotocatalysts into the visible light region. This is particularimportant for example in the field of heterogeneous photocatalysis suchas photolytic hydrogen production or photocatylytic water production orphotocatalytic destruction of organic pollutants. In using the approachin accordance with the present invention, the number of dyes that can bepotentially used in such applications is strongly increased. Moreover,the synthesis of such dyes is surprisingly simple.

The dyes according to the present invention show high quantum efficiencysimilar to that of the standard red-dye. If one therefore combines thedyes of the present invention with other dyes, such as other organicdyes or standard red dye or standard black dye, a broad range of thesolar spectrum may be harvested. That makes the dyes of the presentinvention very promising to be used together with other dyes, such asorganic dyes, standard red dye or standard black dye or further dyesaccording to the present invention with absorption maxima at differentwavelengths. A dye sensitized solar cell comprising a dye according tothe present invention, and, in addition thereto, one or more furtherdyes, is herein also referred to as a multiple-dyes sensitized solarcell (M-DSSC). Preferably, said one or more further dyes is also a dyeaccording to the present invention.

Further, organic dyes have high absorption coefficients. This means itneeds less amount of dye to absorb the same amount of light. Less amountof one dye on a surface enables the use of more dyes with differentabsorption properties, ideally being a mixture of dyes absorbing thewhole range of the sun spectrum.

Furthermore, reference is made to the figures, wherein

FIG. 1 shows a synthesis scheme of one example dye in accordance withthe present invention being represented by general formula 2e, E beingCl or an alkoxy group, preferably ethoxy, propoxy, iso-propoxy orbutoxy, X being as defined above, chromophore being as defined above,

FIG. 2 shows a synthesis scheme of one example dye in accordance withthe present invention being represented by general formula 2h, E, Y, X,n₁, n₂, p, chromophore being as defined above, Hal⁻ being I⁻, Cl⁻, Br⁻,NCS⁻ or SCN⁻,

FIG. 3 shows a synthesis scheme of one example dye in accordance withthe present invention being represented by general formula 5, E, Z,R₁₁-R₁₃, X being as defined above,

FIG. 4 shows a synthesis scheme of one example dye in accordance withthe present invention being represented by general formula 9, X, Y, Z,R₁ being as defined above,

FIG. 5 shows the molecular structure of some dyes according to presentinvention,

FIG. 6 shows the synthesis of one example dye in accordance with thepresent invention being represented by formula 1,

FIG. 7 shows the synthesis of one example dye in accordance with thepresent invention being represented by formula 2,

FIG. 8 shows the synthesis of one example dye in accordance with thepresent invention being represented by formula 5,

FIG. 9 shows a photograph of the adsorption of dye in accordance withthe present invention being represented by formula 1 on a TiO₂ layer,

FIG. 10 shows a table indicating the performance of a dye sensitizedsolar cell prepared with a dye in accordance with the present inventionbeing represented by formula 1 by measuring the efficiency of solarcells by means of sulphur lamp,

FIG. 11 shows the incident photon to current efficiency (IPCE) plottedagainst wavelength for a dye in accordance with the present inventionbeing represented by formula 1,

FIG. 12 shows a table displaying the performance of various dyesensitized solar cells prepared with a dye in accordance with thepresent invention being represented by formula 1 in mixture with otherdyes and in comparison to other sensitizers,

FIG. 13 shows the incident photon to current efficiency of a dye inaccordance with the present invention being represented by formula 1, ofa dye being represented by formula 14 (FIG. 15) and a mixture of thesetwo dyes, plotted against wavelength,

FIG. 14 shows a table indicating the performance of a dye sensitizedsolar cell prepared with a dye in accordance with the present inventionbeing represented by formula 1 in comparison with organic dye beingrepresented by formula 16 (FIG. 15), by measuring the efficiency ofsolar cells by means of sun simulator,

FIG. 15 shows the structure of other sensitizers that were used forcomparison and in mixture with dyes according to present invention(sensitizers 14, 15 and 16).

FIG. 16 shows structures 17-26 which are exemplary dyes in accordancewith the present invention.

FIG. 17 shows exemplary structures 15, 27-32 of other dyes which can beused together with the dyes in accordance with the present invention.

FIGS. 18-20 show various tables and IPCE curves showing the efficienciesof solar cells, as prepared and described in Examples 11) to 13).

FIG. 21 shows various embodiments of electronic devices in accordancewith the present invention wherein energy supply devices, such as solarcell panels, preferably dye sensitized solar cell panels (DSSCs) havebeen incorporated.

Moreover reference is made to the following examples which are given toillustrate, not to limit the present invention.

EXAMPLES 1) Synthesis of One Embodiment of a Dye in Accordance with thePresent Invention, in this Case Dye 1

FIG. 6 shows the synthesis scheme of dye 1 in accordance with thepresent invention.

An equimolar amount of 1 a and diethylester derivative of squaric acid 1b in ethanol is heated in presence of small amount triethylamine to 70°C. for 4 h. The solvent is removed and the crude product is purified bycolumn chromatography on silica gel with n-hexane/ethylacetate as eluentto yield the pure product 1 c.

In next step, to derivative 1 c in ethanol aqueous NaOH is added and themixture stirred for 2 h at 50° C. After cooling, aq. HCl is added andthe solvent is removed. The crude product is purified by columnchromatography on silica gel with dichloromethane/methanol as eluent.The dye 1 in accordance with the present invention is isolated as yellowsolid.

2) Synthesis of One Embodiment of a Dye in Accordance with the PresentInvention, in this Case Dye 2

FIG. 7 shows the synthesis scheme of dye 2 in accordance with thepresent invention.

An equimolar amount of 2 a and diethylester derivative of squaric acid 1b in ethanol and in presence of small amount triethylamine is heated to80° C. for 6 h. The solvent is removed and the crude product is purifiedby column chromatography on silica gel with n-hexane/ethylacetate aseluent to yield the pure intermediate 2 b.

In next step, to 2 b in ethanol aqueous NaOH is added and the mixturestirred for 2 h at 50° C. After cooling, aq. HCl is added and thesolvent is removed. The crude product is purified by columnchromatography on silica gel with dichloromethane/methanol as eluent.The dye 2 in accordance with the present invention is isolated asyellow-orange solid.

3) Synthesis of One Embodiment of a Dye in Accordance with the PresentInvention, in this Case Dye 5

FIG. 8 shows the synthesis scheme of dye 5 in accordance with thepresent invention.

An equimolar amount of brominated derivative 5 a and diethylesterderivative of squaric acid 1 b in ethanol and in presence of smallamount triethylamine is heated to 80° C. for 6 h. The solvent is removedand the crude product is purified by column chromatography on silica gelwith n-hexane/ethylacetate as eluent to yield the pure intermediate 5 b.

In a next step, to a mixture of 5 b in of toluene/methanol, 1.2equivalents of thienyl boronic acid, 1 mol % Pd-catalyst, 10 equivalentsK₂CO₃ are added. The mixture is allowed to stir at 120° C. for 12 h.After cooling the solvent is evaporated. The crude product is purifiedby column chromatography on silica gel with n-hexane/ethylacetate aseluent to yield pure 5 c.

In a subsequent reaction to 5 c in ethanol, aqueous NaOH is added andthe mixture stirred for 2 h at 50° C. After cooling, aq. HCl is addedand the solvent is removed. The crude product is purified by columnchromatography on silica gel with dichloromethane/methanol as eluent.The pure dye 5 in accordance with the present invention is isolated asorange solid.

4) Analytical Data of Dye 1

C18H19NO3 (297.36)

¹H NMR (400 MHz, MeOD): δ=14.8 (s, 1H, —OH), 7.27-7.20 (m, 2H, arH),6.98-6.92 (m, 2H, arH), 5.70 (s, 1H, ═CH—), 3.95 (t, 2H, N—CH2),1.84-1.75 (m, 2H, CH2-Pr), 1.65 (s, 6H, arCH3), 1.06 (t, 6H, CH3-Pr)

ESI MS m/z=297.8 [M+].

UV/VIS (acetonitrile): λmax=404 nm.

5) Effective Adsorption of the Dye on TiO2

FIG. 9 shows a photograph of the adsorption of dye 1 in accordance withthe present invention on a TiO₂ layer

For device preparation, the substrate with screen printed nanoporousTiO2 particles is poured and kept in a dye or dyes mixture solution forat least 1 h. The dye molecules having the acyloin group as anchor groupare able to adsorb onto the nanoporous layer via self-assembling. Theeffective adsorption and chemisorption (covalent coupling) of the dyeswith acyloin group onto semiconductor surface is proved by the stablecolor of the substrate even after the substrate was washed with anorganic solvent.

6) General Protocol for Preparing Solar Cells

The DSSCs are assembled as follows: A 30-nm-thick bulk TiO₂ blockinglayer is formed on FTO (approx. 100 nm on glass or flexible substrate).A 5-30 μm-thick porous layer of TiO₂ semiconductor particles of 0.1882cm² active area multi-printed by screen printing on the blocking layerand sintered at 450° C. for half an hour. Dye molecules are adsorbed tothe nanoporos particles via self-assembling out of a dye-solution. Thedye-solution consists of a single dye or single dye and an additive,such as deoxycholic acid or a mixture of dye in different ratio or amixture of dye in different ratio and an additive. The porous layer isfilled with liquid electrolyte containing I⁻/I₃ ⁻ as redox couple (15mM) by drop casting. A reflective platinum back electrode is attachedwith a distance of 6 μm from the porous layer.

7) Measuring the Efficiency of DSSCS Containing at Least One of theSensitizer Dye Produced by the Method of the Present Invention

The quality of the cells is evaluated by means of current density (J)and voltage (V) characteristics under illumination with light from

a) a sulphur lamp (IKL Celsius, Light Drive 1000) with an intensity of100 mW cm². If not otherwise stated, the results are averages over threecells.

b) a sun simulator (AM1.5G YSS-150) with an intensity of 100 mW cm⁻².

If not otherwise stated, the results are averages over three cells.

The efficiency of a photovoltaic device is calculated as follows:

η=P _(out) /P _(in) =FF×(J _(SC) ×V _(OC))/(L×A)

with FF=V_(max)×I_(max)/V_(oc)×I_(sc)FF=fill factorV_(OC)=open circuit voltageJ_(SC)=short current densityL=intensity of illumination=100 mW/cm²A=active area=0.24 cm²V_(max)=voltage at maximum power pointJ_(max)=current at maximum power point

An important parameter for judging the performance of a dye assensitizer in DSSC is the IPCE curve. The IPCE curve reflects thephoto-activity of the sensitizer dyes at different wavelengths(IPCE=incident photon to current efficiency).

The respective structure of the dyes is given in FIGS. 5 and 15.

8) Efficiency of the DSSC by Using Dye 1 as Sensitizer

The performance and the efficiency of DSSCs prepared by method describedin 6 and measured by method described in 7a with dye 1 are shown in FIG.10. FIG. 11 shows the IPCE plotted verses wavelength for sensitizer 1.

The efficiency of the DSSC prepared with sensitizer dye 1 shows highefficiency (>7%). There are only few other organic dyes, such as dye 16,showing such high performance. However, the superiority of the dyesaccording to present invention lies not only in the high efficiencies ofthe DSSCs achieved when using these dyes, but also in their simplepreparation (FIGS. 1-4).

The highest achievable IPCE value is 1.0. Sensitizer dye 1 shows an IPCEvalue of 0.9 in its maximum at ca. 490 nm. That means that the photonsabsorbed in this region from the sun can be converted to almost 90% tocurrent by injection into conduction band of TiO₂. Such a high value israrely achieved and only with few dyes, such as the Ruthenium basedstandard red dye.

9) Efficiency of M-DSSC Containing a Mixture of Dye 1 and the OrganicDye 14, and a Mixture of Dye 1 and Standard Black Dye 15

The solar cells were prepared by method described in Example 6 andmeasured according to Example 7a. For comparison also DSSCs preparedwith the respective single sensitizer dye were prepared and measured.

The performance and the efficiency of DSSCs are shown in FIG. 12.

A mixture of the dye in accordance with the present invention, in thiscase dye 1, with either an organic dye 14 or with a Ruthenium based dye(black dye) 15 yields an increase in short current density and thus, adrastic increase in DSSC efficiency.

FIG. 13 shows the IPCE curve of the individual dyes 1 and 14, and theIPCE curve of a 1:1 mixture of these dyes. The individual dyes arephoto-active in different region of the solar spectrum. By using amixture of the dyes, due to additive behaviour of the IPCE curves, avery broad range solar light can be harvested and converted to current.

10) Comparing Efficiency of the DSSC Prepared with Dye According toPresent Invention, Namely Dye 1, and Another Organic Sensitizer 16 BothHarvesting Light in the Same Range of the Solar Spectrum

The DSSCs were prepared by method described in Example 6 and measuredaccording to Example 7b.

The DSSC efficiencies are in the same range of 5%. However, when onecompares the structure of the dyes, it becomes clear that the dyeaccording to present invention, namely dye 1, is much more easilysynthesized than dye 16.

11) Efficiency of the DSSC by Using Dye 9 and 2 as Sensitizer

The DSSCs were prepared by the method described in Example 6 and byusing 25 μm TiO₂ layer and measured according to Example 7b. Theefficiency and IPCE curve are shown in FIGS. 18 a and 18 b,respectively.

The IPCE curve reflects the photo-activity of the sensitizer dyes atdifferent wavelengths (IPCE=incident photon to current efficiency). Thehighest achievable IPCE value is 1.0. Sensitizer dye 1, 9 and 2 showvery high, of almost unity, and wide IPCE values.

12) Performance of Solar Cells Prepared with a Mixture of the RespectiveDye and Standard Ruthenium Black Dye 15

The solar cells were prepared by method described in Example 6 andmeasured according to Example 7b. For comparison also DSSC prepared withthe respective single sensitizer dye 15 was prepared and measured. Theefficiency is shown in FIG. 19. As can be seen, the efficiencies byusing a mixture of dyes for sensitization are much higher than thatusing only a single dye as sensitizer.

13) Performance of Solar Cells Prepared with a Mixture of the RespectiveDye and Organic Dye 14

The solar cells were prepared by method described in Example 6 andmeasured according to Example 7b. For comparison also DSSC prepared withthe respective single sensitizer dye 14 was prepared and measured.

-   -   a) by using 26 μm TiO₂ layers as electrode; the efficiency is        shown in FIG. 20 a.    -   b) by using 10 μm TiO₂ layers as electrode; the efficiency is        shown in FIG. 20 b.

The efficiencies on thinner layer are slightly lower than on thick TiO2layer, but, contrary to Ruthenium based sensitizers, still high enoughto show the good performance of the dyes. This is attributed to thestrong light absorption property of the dyes according to claim 1-12. Inboth cases, thin or thick TiO2 layers, the efficiency is increased byusing a mixture of dyes for sensitization compared to that using asingle dye.

The present invention provides for new sensitizer dyes which are usefulfor being employed in solar cells as well as in photocatalyticapplications. They readily adsorb to nanoporous semiconductor layers andare easily manufactured. The use of an acyloin group as anchoring groupfor chromophores in such applications, to the best knowledge of thepresent inventors, has never been reported before.

The features of the present invention disclosed in the specification,the claims and/or in the accompanying drawings, may, both separately,and in any combination thereof, be material for realizing the inventionin various forms thereof.

1. A dye, comprising a chromophore to which an acyloin group isattached, and represented by formula (1a) or (1b):

wherein said chromophore is an organic or metal-organic compoundabsorbing electromagnetic radiation in a range from 300-1200 nm, orwherein A is selected from the group consisting of H, a cyclic alkyl, anacyclic alkyl, a straight or branched chain moiety of formula—(CH₂)_(n1)—R, —[(CR═CR)_(n1)—(CH₂)_(n2)]_(p)—R,—[(C≡C)_(n1)—(CH₂)_(n2)]_(p)—R, —[(CH₂)_(n1)—X_(n2)]_(p)—R, a halogen,moiety comprising at least one heteroatom, a substituted phenyl, anun-substituted phenyl, a substituted biphenyl, an unsubstitutedbiphenyl, a substituted heteroaryl, an unsubstituted heteroaryl, and amoiety forming a ring structure with said acyloin group, wherein, ateach occurrence and independently, n1 and n2=0-12, p=0-6, wherein X is—CR₂, O, S, NR, —CR, wherein R is selected from the group consisting ofH, a straight or branched alkyl chain of formula —C_(n)H_(2n+1), —COOR¹,—OR¹, —SR¹, —NR¹ ₂, F, Cl, Br, I, O, N, NO₂, CN, and CF₃, wherein R¹ isH or a straight or branched alkyl chain of formula —C_(n)H_(2n+1), or asubstituted or non-substituted phenyl or biphenyl, heteroaryl, andn=0-12.
 2. The dye of claim 1, represented by formula (2a), (2b), (2c),(2d), (2e), (2f), (2g), (2h), (2i), or (2j)

wherein Y, at each occurrence, is independently —CR₂, O, S, NR, or —CR.3. The dye of claim 2, represented by formula 2d, 2e, 2f, or 2h.
 4. Thedye of claim 1, wherein said chromophore is selected from the groupconsisting of moieties shown in group 3

or any combination of the moieties of group 3, wherein said chromophoreis linked to said acycloin group by any of the C-atoms or X or Y or Rwithin said chromophore, wherein Z is one or more moieties which, ateach occurrence, is independently selected from the group consisting ofH, a cyclic alkyl, an acyclic alkyl, a straight or branched chain moietyof formula —(CH₂)_(n1)—R, —[(CR═CR)_(n1)—(CH₂)_(n2)]_(p)—R,—[(C≡C)_(n1)—(CH₂)_(n2)]_(p)—R, —[(CH₂)_(n1)—X_(n2)]_(p)—R, a halogen,moiety comprising at least one heteroatom, a substituted phenyl, anunsubstituted phenyl, a substituted biphenyl, an unsubstituted biphenyl,a substituted heteroaryl, and an unsubstituted heteroaryl.
 5. The dye ofclaim 4, represented by formula (5)

wherein R₁₁, R₁₂, R₁₃, at each occurrence, are independently selectedfrom the group consisting of H, a straight or branched alkyl chain offormula —C_(n)H_(2n+1), —COOR¹, —OR¹, —SR¹, —NR¹ ₂, F, Cl, Br, I, O, N,NO₂, CN, CF₃, wherein R¹ is H or any straight or branched alkyl chain offormula —C_(n)H_(2n+), or any substituted or non-substituted phenyl orbiphenyl, heteroaryl, n=0-12.
 6. The dye of claim 5, represented byformula (6)

or represented by any of structures 17-26:


7. The dye of claim 5, represented by formula (7), (8), (9), (10), (11),(12), or (13):


8. The dye of claim 1, wherein said chromophore is a metal complexselected from the group consisting of u structures represented byformula (14)(L)_(n3)(L′)_(n4)M(Hal)_(n5)  (14), wherein M is Ruthenium Ru, OsmiumOs, or Iridium Ir, Hal is independently Cl, Br, I, CN, or —NCS, n3, n4,and n5 are integers which, at each occurrence, are independently 0-4,and L and L′ are organic heterocyclic ligands comprising nitrogen atomswhich are linked by N-atoms to the respective metal M, and whereineither one of L and L′, or both L and L′ are linked to the acyloin groupby any of the C-atoms within said ligands.
 9. The dye of claim 8,wherein said ligands L and L′ are independently, at each occurrence,mono- or polycyclic, condensed rings or such rings covalently bonded toeach other.
 10. The dye of claim 8, wherein said ligands L and L′ areindependently, at each occurrence, selected from the group consisting of

wherein Z is one or more moieties which, at each occurrence, isindependently selected from the group consisting of H, a cyclic alkyl,an acyclic alkyl, a straight or branched chain moiety of formula—(CH₂)_(n1)—R, —[(CR═CR)_(n1)—(CH₂)_(n2)]_(p)—R,—[(C≡C)_(n1)—(CH₂)_(n2)]_(p)—R, —[(CH₂)_(n1)—X_(n2)]_(p)—R, a halogen, amoiety comprising at least one heteroatom, a substituted phenyl, anunsubstituted phenyl, a substituted biphenyl, an unsubstituted biphenyl,a substituted heteroaryl, and an unsubstituted heteroaryl.
 11. The dyeof claim 1, wherein said chromophore is a metal complex represented byformula (16),(IL″)_(n6)M′  (16), wherein M′ is Palladium Pd, Platinum Pt or NickelNi, n6 being is an integer 0-4, and L″ is an organic heterocyclic ligandcomprising at least one nitrogen atom, said ligand being linked by oneor several of said N-atoms to the respective metal M′, and said ligandbeing linked to said acycloin group by any of the C-atoms within saidligand.
 12. The dye of claim 11, wherein said ligand L″ is selected fromthe group consisting of

wherein Z is one or more moieties which, at each occurrence, isindependently selected from the group consisting of H, a cyclic alkyl,an acyclic alkyl, a straight or branched chain moiety of formula—(CH₂)_(n1)—R, —[(CR═CR)_(n1)—(CH₂)_(n2)]_(p)—R,—[(C≡C)_(n1)—(CH₂)_(n2)]—R, —[(CH₂)_(n1)—X_(n2)]_(p)—R, a halogen, amoiety comprising at least one heteroatom, a substituted phenyl, anunsubstituted phenyl, a substituted biphenyl, an unsubstituted biphenyl,a substituted heteroaryl, and an unsubstituted heteroaryl.
 13. Anelectronic device, comprising the dye of claim
 1. 14. The device ofclaim 13, which is a solar cell further comprising a photoactivesemiconductor porous material.
 15. The device of claim 13, furthercomprising a charge-transporting agent which is a liquid, ionic liquid,polymer gel based, or solid state electrolyte.
 16. The device of claim14, which is a solar cell wherein said dye is chemisorbed to saidphotoactive semiconductor porous material.
 17. The device of claim 13,further comprising at least one other dye.
 18. The device according toclaim 17, wherein said at least one other dye is represented by formula(1c) or (1b).
 19. The device of claim 17, wherein said at least oneother dye selected from the group consisting of structures 15 and 27-32:


20. The device of claim 14, wherein said photoactive semiconductorporous material is at least one selected from the group consisting ofTiO₂, SnO₂, ZnO, Nb₂O₅, ZrO₂, CeO₂, WO₃, Cr₂O₃, CrO₂, CrO₃, SiO₂, Fe₂O₃,CuO, Al₂O₃, CuAlO₂, SrTiO₃, SrCu₂O₂, and ZrTiO₄.
 21. The device of claim20, wherein said photoactive semiconductor porous material has one orseveral of the following features: a thickness of 1-100 μm, consists ofone or more layers comprises particles having an average diameter orlength in a range of from 1 nm to 40 nm, is a mixture of at least afirst particle and second particle, said first particle having anaverage diameter or length in a range of from 1 nm to 30 nm, and saidsecond particle having an average diameter in a range of from 30 nm to100 nm and/or a length in a range of from 100 nm to 5 μm.
 22. Adye-sensitized solar cell comprising a sensitizer comprising the dye ofclaim
 1. 23. The dye-sensitized solar cell of claim 22, furthercomprising at least one other dye.
 24. The dye-sensitized solar cell ofclaim 23, wherein said at least one other dye is represented by formula(1a) or (1b) or a dye selected from structures 15, 27-32:


25. A method of photocatalyzing a reaction, the method comprising:exposing a component of the reaction to light in the pressure of the dyeof claim
 1. 26. The dye of claim 1, wherein the chromophore absorbselectromagnetic radiation in a range from 350-500 nm.
 27. The dye ofclaim 1, wherein the chromophore absorbs electromagnetic radiation in arange from 500-750 nm.
 28. The dye of claim 4, wherein at least one Z ofthe chromophore is a moiety of group 4: